Method and structure to improve properties of tunable antireflective coatings

ABSTRACT

A method for improving the properties of tunable etch resistant anti-reflective coatings (TERA) is disclosed. The method includes annealing the deposited layer of TERA in an environment containing at least one of hydrogen and deuterium. The annealed layer has an increased concentration of hydrogen and/or deuterium as compared to the deposited film, and may also have an additional concentration of hydrogen or deuterium at the interface between the substrate and the layer of TERA.

BACKGROUND OF INVENTION

The present invention is directed to structures and methods useful forfabricating integrated circuits (ICs), in particular structures having aplurality of interconnect layers. More particularly, the presentinvention is directed to a method for improving the properties oftunable vapor deposited materials which function as antireflectivecoatings and/or as hardmasks for high resolution lithography.

The semiconductor industry continues to require devices with anincreased device density and a concomitant decrease in device geometry.The continuous size reduction of the critical dimension (CD) ofsemiconductor devices creates an increasing challenge to balance theneed for efficient etch resistance (i.e. resist thickness) with thedemands of production-worthy depth-of-focus (DOF). Resist thickness iscontinuously thinned to accommodate reduced DOF which results from useof tools with higher numerical aperture (NA). As the thickness of theresist is decreased, the resist becomes less effective as a mask forsubsequent dry etch image transfer to the underlying substrate, i.e.most if not all of the resist is etched away during the subsequentpattern transfer process. Without significant improvement in the etchselectivity exhibited by current single layer resists (SLR), thesesystems can not provide the necessary lithographic and etch propertiesfor high resolution lithography.

Another problem with single layer resist systems is critical dimension(CD) control. Substrate reflections at ultraviolet (UV) and deepultraviolet (DUV) wavelengths are notorious to produce standing waveeffects and resist notching which severely limit CD control of singlelayer resists. Notching results from substrate topography andnon-uniform substrate reflectivity which causes local variations inexposure energy on the resist. Standing waves are thin film interference(TFI) or periodic variations of light intensity through the resistthickness. These light variations are introduced because planarizationof the resist presents different thickness through the underlyingtopography. Thin film interference plays a dominant role in CD controlof single layer photoresist processes, causing large changes in theeffective exposure dose due to a tiny change in optical phase.

Various antireflective coating (ARC) and hardmask materials have beendeveloped to alleviate these problems of etch resistance and substratereflections. Such materials include the tunable vapor depositedmaterials described in U.S. Pat. No. 6,316,167, the disclosure of whichis incorporated herein by reference. These tunable materials have thecomposition R:C:H:X, wherein R is selected from Si, Ge, B, Sn, Fe, Tiand mixtures of these elements, and X is selected from 0, N, S, F andmixtures of these elements, and X is optionally present. These materialswill be referred to as tunable etch resistant ARC, or TERA. Compared toother hardmask materials such as polysilicon, TERA exhibits excellentetch selectivity to resist and to oxide. Selectivity of 1:2.5 to resistand 7:1 to oxide has been demonstrated. TERA is also envisioned as anantireflective layer, so no additional ARC is required for lithographyprocesses using TERA. Thus, the mask open process is simplified,resulting in cost reduction.

However, lithography processes using TERA have been found to suffer froma large variation of CD post lithography, which limits a successfulimplementation of TERA as hardmask. The CD variation is attributed tothe nonuniformity of as-deposited TERA properties across the wafer.Thus, there is a need in the art for a method to improve TERA uniformityand reduce CD variation across the wafer.

SUMMARY OF INVENTION

The aforementioned deficiencies of the prior art are alleviated throughuse of the method of the present invention. Specifically, the presentinvention is directed to a method for improving TERA uniformity byannealing a wafer comprising a TERA film in an environment comprisinghydrogen or deuterium, an isotope of hydrogen. Up to 40% CD variationreduction on TERA wafers is demonstrated.

The present invention is specifically directed to a method comprising:depositing on a surface of a substrate a layer formed of a material; andannealing the layer in an environment comprising at least one ofhydrogen and deuterium, thereby forming an annealed layer. The materialcomprises carbon, at least one of hydrogen and deuterium, and at leastone element selected from the group consisting of Si, Ge, B, Sn, Fe andTi. The material may further comprise at least one element selected fromthe group consisting of O, N, S and F.

The present invention is also directed to a lithographic structurecomprising a plurality of layers, at least one layer being formed of amaterial comprising carbon, deuterium, and at least one element selectedfrom the group consisting of Si, Ge, B, Sn, Fe and Ti. The material mayfurther comprise at least one element selected from the group consistingof O, N, S and F, and also may further comprise hydrogen.

BRIEF DESCRIPTION OF DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The drawings are for illustration purposes only and arenot drawn to scale. Furthermore, like numbers represent like features inthe drawings. The invention itself, however, both as to organization andmethod of operation, may best be understood by reference to the detaileddescription which follows, taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1(a)-1(d) illustrate a preferred embodiment of the method of thepresent invention;

FIGS. 2(a)-2(b) illustrate two alternate embodiments for the annealingstep of the present invention;

FIG. 3 illustrates an embodiment of annealed layer of the presentinvention; and

FIGS. 4(a)-4(b) illustrate the results of an example of the presentinvention.

DETAILED DESCRIPTION

The invention will now be described by reference to the accompanyingfigures. In the figures, various aspects of the structures have beenshown and schematically represented in a simplified manner to moreclearly describe and illustrate the invention. For example, the figuresare not intended to be drawn to scale. In addition, the verticalcross-sections of the various aspects of the structures are illustratedas being rectangular in shape. Those skilled in the art will appreciate,however, that with practical structures these aspects will most likelyincorporate more tapered features. Moreover, the invention is notlimited to constructions of any particular shape.

The invention is directed to a method to improve the uniformity of afilm such as TERA, thus improving the lithography and etchingperformance of the film by annealing the deposited film in anenvironment containing hydrogen or deuterium.

A preferred embodiment of the method of this invention is illustrated inFIGS. 1(a)-1(d). The method begins in Figure 1(a) with a substrate 10which may be, for example, a bare silicon wafer, a wafer containing oneor more layers of other materials, or a wafer containing various devicestructures.

In FIG. 1(b), a layer 11 of a material such as TERA is deposited onsubstrate 10. In general, the layer 11 may be formed of a material suchas the tunable vapor deposited materials described in U.S. Pat. No.6,316,167, the disclosure of which has been incorporated herein byreference. These tunable vapor deposited materials have a structuralformula R:C:H:X, wherein R is selected from the group consisting of Si,Ge, B, Sn, Fe, Ti and combinations thereof, and wherein X is not presentor is selected from the group consisting of one or more of O, N, S andF. Alternatively, layer 11 may be formed of a material having astructural formula R:C:H:D:X or R:C:D:X, where R and X are as definedabove, and D is deuterium.

Layer 11 may be deposited by any suitable method, including the methodsdescribed in U.S. Pat. No. 6,316,167, the disclosure of which has beenincorporated herein by reference. For example, layer 11 may be depositedby plasma enhanced chemical vapor deposition (PECVD) techniques. In onetype of technique the PECVD process is performed in a parallel platereactor where the substrate is placed on one of the electrodes. Variousexemplary deposition embodiments are disclosed in U.S. Pat. No.6,316,167.

When layer 11 is formed of a material having structural formula R:C:H:X,each component is preferably present in the following amounts. Thepreferred atomic % ranges for R are the following: preferably 0% to 95%,more preferably 0.5% to 95%, most preferably 1 to 60% and most highlypreferably 5 to 50%. The preferred atomic % ranges for C are thefollowing: preferably 0% to 95%, more preferably 0.5% to 95%, mostpreferably 1 to 60% and most highly preferably 5 to 50%. The preferredatomic % ranges for H are the following: preferably 0% to 50%, morepreferably 0.5% to 50%, most preferably 1 to 40% and most highlypreferably 5 to 30%. The preferred atomic % ranges for X are thefollowing: preferably 0% to 70%, more preferably 0.5% to 70%, mostpreferably 1 to 40% and most highly preferably 5 to 30%.

Alternatively, some or all of the hydrogen in the R:C:H:X material maybe replaced with deuterium, such that layer 11 is formed of a materialhaving structural formula R:C:H:D:X or R:C:D:X. Layer 11 containingdeuterium may be formed by using a precursor material containingdeuterium in place of some or all of the hydrogen.

The method of this invention continues with layer 11 being annealed inan environment containing hydrogen or deuterium. In FIG. 1(c), theannealing step is shown in an environment containing hydrogen. In analternative embodiment, the annealing step may be performed in anenvironment containing deuterium. The annealing environment preferablycontains 0.1% to 100% hydrogen and/or deuterium. One or more other gasessuch as, for example, nitrogen, helium, neon or argon, may be present inthe annealing environment.

The annealing temperature is preferably 350° C. to 500° C., morepreferably 380° C. to 450° C., and most preferably 400° C. to 425° C.The annealing duration is preferably 1 min. to 100 min., more preferably10 min. to 60 min., and most preferably 30 min.

The annealing process may be performed as a separate step afterdeposition. Alternatively, the annealing may be performed in situ, i.e.,in the same chamber as the deposition process. These two embodiments areillustrated in FIGS. 2(a) and 2(b), which are graphs of the wafertemperature versus time during the method of this invention. Arepresents the temperature of the substrate prior to deposition of layer11, B represents an elevated temperature typically encountered in adeposition chamber during deposition of layer 11, C represents a loweredtemperature of the wafer as the wafer is transferred from the depositionchamber to another chamber or furnace for annealing, D represents anelevated temperature during anneal, and E represents a loweredtemperature of the wafer which is ready for further processing. In FIG.2(a), the annealing process is performed in a separate chamber orfurnace, whereas in FIG. 2(b), deposition and annealing are performed inan integrated process in the same chamber or tool.

Following anneal of layer 11, processing of the wafer may continue. Forexample, as shown in FIG. 1(d), photoresist 12 may be deposited on layer11 and patterned using a conventional lithography process to formopenings 13.

The method of this invention produces a new film structure containingadditional hydrogen and/or deuterium as compared to the deposited film.For example, when deposited layer 11 is formed of a material havingstructural formula R:C:H:X, and layer 11 is annealed in an environmentcontaining hydrogen, the preferred atomic % ranges for H are thefollowing: preferably 2% to 70%, more preferably 20% to 60%, and mostpreferably 30 to 50%. Alternatively, when deposited layer 11 is formedof a material having structural formula R:C:H:X, and layer 11 isannealed in an environment containing deuterium, the preferred atomic %ranges for D are the following: preferably 2% to 70%, more preferably10% to 40%, and most preferably 20 to 30%. In yet another alternativeembodiment, when deposited layer 11 is formed of a material havingstructural formula R:C:D:X, and layer 11 is annealed in an environmentcontaining deuterium, the preferred atomic % ranges for D are thefollowing: preferably 2% to 70%, more preferably 20% to 60%, and mostpreferably 30 to 50%.

Moreover, annealed layer 11 may have an additional concentration ofhydrogen or deuterium at the interface between substrate 10 and layer11. FIG. 3 illustrates an exemplary profile of H or D concentrationacross layer 11 and substrate 10. The solid line represents one possibleH or D profile before anneal, and the dotted line represents anotherpossible profile after anneal showing a peak H or D concentration at theinterface between layer 11 and substrate 10 due to the accumulation of Hor D at the sites of interface defects.

The following example is provided to illustrate the scope of theinvention. Because this example is given for illustrative purposes only,the invention embodied therein should not be limited thereto.

Example: About 2000 Å of a TERA film was deposited on a set of siliconwafers with 53 Å pad oxide, 1800 Å pad nitride, and 15000 Å borosilicateglass (BSG) oxide. The wafers were then divided into three groups. Thefirst group of the wafers was annealed in a furnace containing 10%hydrogen and 90% nitrogen, and the second group of the wafers wasannealed in the same furnace with 100% nitrogen. The annealingtemperature was 400° C. and the annealing duration was 30 min. The thirdgroup of wafers, which was used as a control group, was not annealed.After the annealing step, all wafers were then subjected to the samelithography process. The photoresist layer had a thickness ofapproximately 3500 Å after deposition and approximately 3000 Å afterexposure. The critical dimensions (CDs) of these three groups were thenmeasured and results are compared in FIG. 4. FIG. 4(a) shows that themean CD is very close for all wafers regardless of annealing. Thisindicates that there is no need to change the lithography process whenthe annealing process is added. FIG. 4(b) shows that the across-wafer CDvariation is reduced from about 25 nm without annealing to about 15 nmwith annealing in the environment containing hydrogen. Virtually nochange in CD variation was observed with annealing in the environmentcontaining only nitrogen. The reduction of CD variation is attributed tothe improved TERA uniformity by annealing in an environment containinghydrogen.

While the present invention has been particularly described inconjunction with a specific preferred embodiment and other alternativeembodiments, it is evident that numerous alternatives, modifications andvariations will be apparent to those skilled in the art in light of theforegoing description. It is therefore intended that the appended claimsembrace all such alternatives, modifications and variations as fallingwithin the true scope and spirit of the present invention.

1. A method comprising: depositing on a surface of a substrate a layerformed of a material comprising carbon, hydrogen, deuterium and at leastone element selected from the group consisting of Si, Ge, B, Sn, Fe andTi; and annealing said layer in an environment comprising at least oneof hydrogen and deuterium, thereby forming an annealed layer.
 2. Themethod of claim 1, wherein said material further comprises at least oneelement selected from the group consisting of O, N, S and F. 3.(canceled)
 4. The method of claim 1, wherein said layer is deposited bya plasma enhanced chemical vapor deposition (PECVD) process.
 5. Themethod of claim 4, wherein said PECVD process is performed in a parallelplate reactor wherein said substrate is placed on an electrode of thereactor.
 6. The method of claim 2, wherein said material comprisescarbon in an amount of about 0.5 to 95 atomic %, hydrogen in an amountof about 0.5 to 50 atomic %, at least one element selected from thegroup consisting of Si, Ge, B, Sn, Fe and Ti in an amount of about 0.5to 95 atomic %, and at least one element selected from the groupconsisting of O, N, S and F in an amount of about 0.5 to 70 atomic %. 7.The method of claim 2, wherein said material comprises carbon in anamount of about 1 to 60 atomic %, hydrogen in an amount of about 1 to 40atomic %, at least one element selected from the group consisting of Si,Ge, B, Sn, Fe and Ti in an amount of about 1 to 60 atomic %, and atleast one element selected from the group consisting of O, N, S and F inan amount of about 1 to 40 atomic %.
 8. The method of claim 2, whereinsaid material comprises carbon in an amount of about 5 to 50 atomic %,hydrogen in an amount of about 5 to 30 atomic %, at least one elementselected from the group consisting of Si, Ge, B, Sn, Fe and Ti in anamount of about 5 to 50 atomic 10, and at least one element selectedfrom the group consisting of O, N, S and F in an amount of about 5 to 30atomic %.
 9. The method of claim 1, wherein said annealing environmentcontains at least one of hydrogen and deuterium in an amount of about0.1 to 100%.
 10. The method of claim 1, wherein said annealing isperformed at a temperature of about 350° C. to 500° C. and for aduration of about 1 min. to 100 min.
 11. The method of claim 1, whereinsaid annealing is performed at a temperature of about 380° C. to 450° C.and for a duration of about 11 min. to 60 min.
 12. The method of claim1, wherein said annealing is performed at a temperature of about 400° C.to 425° C. and for a duration of about 30 min.
 13. The method of claim1, wherein said depositing step is performed in a first chamber, andsaid annealing step is performed in a second chamber different from saidfirst chamber.
 14. The method of claim 1, wherein said depositing stepis performed in a chamber, and said annealing step is performed in thesame chamber.
 15. The method of claim 1, wherein said layer is annealedin an environment comprising hydrogen, and said annealed layer compriseshydrogen in an amount of about 20 to 60 atomic %.
 16. The method ofclaim 1, wherein said layer is annealed in an environment comprisinghydrogen, and said annealed layer comprises hydrogen in an amount ofabout 30 to 50 atomic %.
 17. The method of claim 1, wherein said layeris annealed in an environment comprising deuterium, and said annealedlayer comprises deuterium in an amount of about 10 to 40 atomic %. 18.The method of claim 1, wherein said layer is annealed in an environmentcomprising deuteriun, and said annealed layer comprises deuterium in anamount of about 20 to 30 atomic %.
 19. The method of claim 1, whereinsaid annealed layer comprises at least one of hydrogen and deuterium ina concentration which is greater at an interface with said substratethan at other portions of the layer.
 20. A method comprising: depositingon a surface of a substrate a layer formed of a material comprisingcarbon, deuterium and at least one element selected from the groupconsisting of Si, Ge, B, Sn, Fe and Ti; and annealing said layer in anenvironment comprising at least one of hydrogen and deuterium, therebyforming an annealed layer. 21-23. (canceled)